40 ‘Glee’ Cast Members And Guest Stars You Completely Forgot About

Remember when Gwyneth Paltrow kinda-sorta had a singing career? After showcasing her talents in her Country Strong role, Gwyneth stopped by William McKinley High as Holly Holiday, Mr. Schue's substitute, in season two.

Who else would judge the Glee Club Nationals in season three other than Lindsay Lohan? And the New Directions have the actress partly to thank for their trophy at the end of the episode.

Perez Hilton was also sitting behind the judges' table at Nationals in season three. But the celebrity blogger gets into trouble with Lindsay Lohan when he doesn't stop posting about what she was doing.

Not to be confused with Brittany S. Pierce, the pop princess appeared as herself (well, in a Cheerios uniform) in a season two episode that recreated (sometimes almost frame-for-frame) some of her iconic moments.

A musical TV show isn't a musical TV show until Idina Menzel stops by to belt out some tunes. The Broadway star caused a little bit of drama in season one as the coach of Vocal Adrenaline, the Glee club's archrivals, and she eventually turned out to be Rachel's biological mother. Then, you know, there was that whole "adopting Quinn and Puck's baby and then forming a questionable relationship with Puck" thing in season two.

The legendary newscaster starred as herself in season two, on assignment at McKinley High School to name Sue Slyvester "Loser of the Year."

Katie told the Wall Street Journal before her guest appearance that viewers who were hoping for the TV host to break into song would be disappointed. "I just had so much fun. I joked with some press that I would be doing a Busby Berkeley-like number, but it was just that, a joke" she said. "Singing and dancing are not my hidden talents, I can assure you."

Rachel had to get all that showbiz ambition from somewhere, and it all starts to make sense when you see one of her dads Hiram Berry is played by Jeff Goldblum. After audiences heard about the characters' dads for three seasons, the Jurassic Park actor made the wait worth it.

When some of the Glee cast moves to New York in season five, they meet Elliot "Starchild" Gilbert, played by Adam Lambert. The American Idol runner-up quickly gets entangled in the group's antics, including joining Kurt's band and offering a place for Rachel to stay when she's feuding with her then-roommate Santana.

"I had such a blast filming the show, and loved getting back into acting and working with such great people," he told The Hollywood Reporter. "I'm so excited for everyone to see it!"

Legendary actress Carol Burnett starred as Sue's mom, and while she only had scenes with Jane Lynch (including a duet of Ohio), the comedian said she watched other scenes and was blown away by what she saw. "During a break I watched them do a tribute to 'Singin' in the Rain,'" she told TV Guide. "I said, 'My God, it really is like going back to the good old days with Gene Kelly and Fred Astaire.'"

You might remember more than how to ask "Where is the library?" if every high school Spanish class included Ricky Martin as the teacher singing "Sexy And I Know It" as the day's instruction. The Grammy winner appeared in the third season of the show.

In the epic showdown between high school nemeses Mr. Shue and Bryan Ryan (NPH), who will come out on top? But really, considering their powerhouse duet cover of Aerosmith's "Dream On," everyone's a winner.

As Dean of Vocal Performance and Song Interpretation at New York Academy of the Dramatic Arts Carmen Tibideaux, Whoopi Goldberg is often seen in the audience, delivering strict criticism to Rachel and Kurt. But since it is Whoopi, every moment with the EGOT winner is gold.

If you only get one complaint about the Mr. Shue-Emma relationship, it might as well be that it meant you only got to see John Stamos as sexy dancing dentist Carl Howell for one season of Glee.

The two end up getting married in Vegas, but when it's revealed that Emma is still confused about her feelings for Will, Carl moves into a hotel. “It’s really nice that this show worked," John told Entertainment Weekly. "They goofed on me in the beginning, so I had to secretly watch it, because I loved it so much. I told everybody I hated it, but I was a closet Glee fan.”

While Stephen Hawking might be Brittany's biological dad, Ken Jeong joined the show in its final season as Brittany's stepfather, Pierce Pierce.

Things never go great for members of New Directions when Josh Groban shows up. In season one, the multi-platinum artist did attend one of the Acafellas' performances (Mr. Shue's side project) but was really only there to serve one of the members a restraining order. He then ended up hitting on Mr. Shue's wife, and Josh later appeared as one of the judges at regionals.

After Kurt described her character as "the coolest socialite in the world," June Dolloway could be played by no one else but the iconic Shirley MacLaine. The legend starred in season five as a wealthy NYADA donor who takes a special interest in Blaine.

"That they can do so much in so little time," Shirley told Entertainment Weekly about what surprised her on set. "Really, it’s a shock. And for me, too! I am surprised at that. Someone like me, who was trained my whole life with a sense of understanding that creativity takes time. But I expected it would be fun, because a musical environment is always fun for me."

The Alias star stopped by Lima, Ohio, as Mr. Schue's father for one episode in season one.